1. Field of the Invention
The present invention relates to data center cooling efficiency. In particular, it relates to a method for enhancing the cooling efficiency of computer room air conditioning units.
2. Description of the Related Art
Raised floors are used in data centers to create a space between a sub-floor of the building and the normal working environment of the computer room. The space between the sub-floor and the raised floor panels creates an under-floor cool-air circulating plenum for thermal management of the data processing servers installed in banks of rack systems on top of the raised floor. The floor panels, themselves, are either solid or perforated. Of the perforated panels, manufacturers have made new design changes in an effort to increase the available open area of the panels, in order to increase the air flow of cooling air throughout the room. These efforts have led to the production and use of air-grate raised floor panels.
Air-grate panels use an open frame design so that cooling air, originating in the under floor, or lower, plenum flows upwardly through the openings in the air-grate frame and into the computer room in order to aid in cooling the server racks installed on top of the raised floor. The air-grate panels may also include perforated top plates, connected to the air-grate structural frame members, in order to provide a variety of different working surfaces having a desired aesthetic appearance, or with the perforations, or openings, in the plate configured so as comply with certain federal and state regulations, as they relate to occupational safety and/or persons with disabilities, or to increase air flow and cooling efficiency.
Overall, the cooling components, of a computer room, are charged with creating, and moving air on the data center floor. From there, the room itself must maintain separate climates in relation to the cool air, which is required by the servers, and the hot air which they exhaust. Without separate boundaries, the air paths mix, resulting in both economic and ecological consequences. Air-grate panels are thus key cooling components in the overall design and construction of computer rooms. With a raised floor, the use of air-grate panels is a way to separate the computer room into a “lower-plenum/upper-plenum” air handling boundary configuration where the cooling air “originates” in the lower plenum, flows upwardly through the openings in the air-grate panels, and is made available to flow through the server doors, for cooling the server racks, installed on the raised floor, in the upper plenum of the computer room. In operation, the data processors heat the air, in the upper plenum, as it flows through the server, where it is returned to the computer room air conditioning units (“CRAC”) for cooling, and recycling the conditioned air back into the lower, or under-floor, plenum.
A further refinement, in the use of air-grate floor panels, came in the early 2000s, when scientists advanced the concept of “hot aisle/cold aisle”, as an additional means for attempting to achieve air separation within the server room. This design uses a system which includes three basic components to achieve hot aisle/cold aisle separation. Those components involve the use of air conditioners, fans and perforated raised floor panels in combination to act synergistically in the construction of a cooling infrastructure, as a means to separate and contain the inlet cold air and the exhaust hot air. With this approach, the racks are supported on a raised floor and are connected into a series of rows. The fronts of the racks face each other and become the cold aisles, as a result of the inherent front-to-back heat dissipation of most IT equipment. The CRAC's are positioned around the perimeter of the room, or at the end of hot-aisles, so that they push cold air under the raised floor and through the cold aisle. The perforated raised floor panels are placed only in the cold aisles which concentrates cool air to the front of racks in order to get sufficient air flow into the server intake. In this manner, all of the servers should be mounted so that their server door air intake is facing the front of the rack, and their exhaust door is facing the rear. As the air moves through the servers, it is heated and eventually dissipated into the hot aisle. The exhaust air is then routed back to the air handlers.
This design, which aligns data center racks into alternating rows, endures in critical facilities throughout the world, and is widely regarded as the first major step in improving airflow management. In use, part of this air flow, or stream, enters the racks and then the equipment, and part of the air flow bypasses the equipment and returns to the air handling units. The air that enters the server doors is heated, and then exhausted through the back of the servers where it is recycled as return air into the air handling units. Typically, some intermixing of the hot and cold air paths is experienced due to improper sealing in the rack, or recirculation above and around the sides of the rack rows.
Other conditions occur which interfere with optimum cooling efficiency in the “hot aisle/cold aisle” constructions, as well. For example, “bypass air” is an interfering condition observed when conditioned air that does not reach computer equipment escapes through cable cut-outs, holes under racks, or misplaced perforated tiles or holes in the computer room perimeter walls. Bypass air limits the precise delivery of cold air at the server door intake. “Hot air recirculation” is also an interfering condition found under conditions where waste heat enters the cold aisle. In order to combat this condition, operators ensure that the cooling infrastructure must throw colder air at the equipment to offset mixing. Another such condition is hot air contamination which prohibits the air handlers from receiving the warmest possible exhaust air, rendering their operation less efficient. Finally, hot spots may persist as a result of any, or all, of the above conditions.
Concomitant with the ever increasing advancements in the volume and speed within which data is processed; data center operators are observing a rise in the energy of the thermal dissipation for the data processor equipment installed in upper plenum of the center. Indeed, the thermal dissipation energy, resulting with the use of such technologies, is now exceeding the operational design limitations, for even the most popular designs of air-grate floor panels in use today, in even those computer rooms which employ the lower-plenum/upper-plenum and hot aisle/cold aisle air separation boundary layer technologies. These uses generate enormous heat loads, on the system, for dissipation, within the same volumetric area, which significantly increases the concentration of heat applied to the internal data processing conductors in the server. For example, it is not uncommon to now experience server racks pushing 7 kw per rack, with operational expectations within the industry of scaling upwards to a 12-30 kw use. Thus, certain manufacturers of air-grate floor panels are experimenting with designs which further increase the available open area of the openings in the air-grate or perforations in the panel top plate. In addition, operators are also working on ways to lower the temperature set-point of the entire data center in order to enhance cooling of those computer servers which are positioned in the upper reaches of the server racks, in the upper plenum. However, the first design solution includes inherent structural load and safety limitations, and the second operational solution significantly drives up the cost in providing electrical utilities to the center.
Another structural solution is directed toward an effort in continuing to redesign the air flow characteristics of the air-grate panels themselves, with an appreciation in both the air flow separation dynamics, when passing through the flat bottom of the slotted air-grate, and also as to air flow passing through the air-grate when installed on a pedestal support system. One such design is illustrated in U.S. Pat. No. D567,398, to Meyer. There, it is ordinarily observed that air scoops are projecting downwardly as part of the superstructure of the air-grate frame. It is readily apparent that the scoop design would act to capture air, as it flows in a generally horizontal direction through the lower plenum of a raised floor. A fluid dynamic, inherent in such design, would result in an increase in the velocity of the air flowing from the lower plenum, as it curves upwardly when passing the scoop, and into the upper plenum, of a computer room, through slotted perforations in the air-grate floor panel plate. This increase in velocity would seem to enhance cooling and further promote the creation of air separation barriers within the computer room.
As mentioned above, the concept of “hot aisle/cold aisle” uses improvements in the design and location of air conditioners, fans, and the raised floors as the cooling infrastructure and focuses on separation of the inlet cold air and the exhaust hot air through the system. However the construction and configuration of the server doors themselves is also a significant parameter in the overall design of the system which has yet to be fully realized. Early versions of server enclosures, often with “smoked” or glass front doors became obsolete with the adoption of “hot aisle/cold aisle” technologies. As a result, the use of perforated doors became necessary for the “hot aisle/cold aisle” approach to work. For this reason, perforated doors remain the standard in the industry for most off-the-shelf server enclosures. Indeed, there exists some debate relating to the total percentage of surface area in the server doors which is required to achieve optimal cooling. For example, certain manufactures have now have established designs which include a percentage of perforation in the range of 65% to over 80% of the total surface area of the door.
While the foregoing methods and materials are useful in providing thermal separation in data centers adopting the hot aisle/cold aisle strategies in the scheme of construction, there still exists a need to provide improvements in the cooling efficiency of the CRAC units. The present invention satisfies these needs.